Monitoring the breathing and/or lung functions of a subject provides data that is often useful for detecting and/or diagnosing the presence of lung disease and/or pulmonary obstructions and/or other conditions. Accurate measurement and analysis of breathing and/or lung functions generally requires the use of devices such as masks or mouthpieces coupled to the mouth of a subject to be monitored. These devices tend to be uncomfortable and/or invasive and do not lend themselves to monitoring difficult and/or frail subjects, for example neonatal subjects.
Respiratory Inductance Plethysmography is another method of monitoring the breathing and/or lung functions of a subject, which is carried out by measuring the movement of the chest and abdominal wall. This approach is based on the theory that the sum of the changes in the anteroposterior diameter of the abdomen and the rib cage correspond to changes in lung volume. Two elastic bands that incorporate sinusoid wire coils are used to measure this diameter. One of the bands is placed around the rib cage under the armpits and the other around the abdomen at the level of the umbilicus.
Expansion of the bands changes the self-inductance of the coils, allowing the change in the anteroposterior diameter to be measured. The bands are connected to an oscillator and demodulation electronics, which convert the readings into digital waveforms. These waveforms are then used to analyse and/or describe various measures of complex respiratory patterns, for example respiratory rate, tidal volume, minute ventilation, peak inspiratory flow, fractional inspiratory time, peak and/or mean inspiratory and/or expiratory flow measures and the percent contribution of the chest and/or abdomen to the tidal volume.
The fitting of the bands on the subject to be monitored requires manoeuvring of the subject, which can in some cases be problematic in difficult and/or frail subjects.
Another known method and associated apparatus for monitoring the breathing and/or lung functions of a subject is disclosed in international publication number WO2010066824 published Jun. 17, 2010 (based on international application number PCT/EP2009/066790 file Dec. 10, 2009 with international phase concluded Jun. 11, 2011) together with an apparatus for carrying out the method, the contents of which are incorporated herein. This method involves an optical measurement of the three-dimensional shape of the body of the subject over time and derives breathing volume data from the changes in shape. Breathing data of the subject may be compared with breathing data associated with healthy and disease states in a statistical database to diagnose the subject's lung function.
It is desirable to provide a method of processing the measurement data that allows a more accurate diagnosis to be made.